This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. xc2xa7119 from my application FUSING DEVICE OF ELECTROPHOTOGRAPHIC IMAGE FORMING APPARATUS filed with the Korean Industrial Property Office on Sep. 6, 2001 and there duly assigned Ser. No. 54804/2001.
1. Technical Field
The present invention relates to a fusing device for an electrophotographic image forming apparatus and, more particularly, to a fusing device using a heat pipe to decrease power consumption and allow flash heating in an electrophotographic image forming apparatus.
2. Related Art
Electrophotographic image forming apparatuses include a fusing device for heating a sheet, to which a toner image is transferred, in order to fuse and fix the toner image in a powder state to the sheet. The fusing device includes a fusing roller for fusing and fixing toner to a sheet and a pressing roller for pressing the sheet against the fusing roller.
A fusing roller unit includes a cylindrical fusing roller and a halogen lamp installed inside the fusing roller and along its axis. A Teflon coating layer is formed on the surface of the fusing roller. The halogen lamp generates heat within the fusing roller, and the fusing roller is heated by the radiant heat emitted from the halogen lamp.
A pressing roller is disposed below the fusing roller unit and in contact with the fusing roller such that a sheet passes therebetween. The pressing roller is elastically supported by a spring so that it can make the sheet closely contact the fusing roller with a predetermined pressure when the sheet passes between the fusing roller and the pressing roller. A toner image formed on the sheet in a powder state is fused and fixed to the sheet by predetermined pressure and heat when the sheet passes between the fusing roller and the pressing roller.
A thermistor for measuring the surface temperature of the fusing roller, and a thermostat for cutting off the supply of power when the surface temperature of the fusing roller exceeds a predetermined set value, are provided at one side of the fusing roller. The thermistor measures the surface temperature of the fusing roller, and transmits an electric signal corresponding to the measured temperature to a controller (not shown) of a printer (not shown). The controller controls the quantity of electricity supplied to the halogen lamp according to the measured temperature so as to maintain the surface temperature of the fusing roller within a predetermined range. When the temperature of the fusing roller exceeds the predetermined set value because the thermistor and the controller fail to control the temperature of the fusing roller, a contact (not shown) of the thermostat opens to cut off the supply of power to the halogen lamp.
Such a fusing device using a halogen lamp as a heat source consumes a large amount of electric power. Particularly, when power is turned on, the device requires quite a long warm-up time. The warm-up time may range from several tens of seconds to several minutes. In addition, in the fusing device, since a fusing roller is heated by radiation emitted from a heat source, heat transmission is slow, and compensation for temperature deviation caused by a decrease in temperature occurring due to contact with a sheet is slow, so that it is difficult to maintain the temperature of the fusing roller constant. Moreover, since electric power must be periodically applied to the heat source in order to maintain the temperature of the fusing roller constant in a standby mode (in which the operation of the printer is in pause), unnecessary electric power is consumed.
To solve the above-described problems, it is an object of the present invention to provide a fusing device, including a power connecting unit having improved durability and reliability, and decreasing warm-up time during initial operation, or during transition from a standby mode to renewed operation, in an electrophotographic image forming apparatus.
To achieve the above object of the invention, there is provided a fusing device for an electrophotographic image forming apparatus. The fusing device includes: a heat pipe having a tubular shape and containing a predetermined amount of a working fluid, the heat pipe being hermetically sealed at both of its ends; a fusing roller surrounding the heat pipe; a heater spirally installed between the fusing roller and the heat pipe for generating heat; and a power connecting unit for transmitting external electric power to the heater. The heater includes: a resistive coil for generating heat using the electric power transmitted from the power connecting unit; an insulation layer covering the resistive coil; a metal layer surrounding the insulating layer; and leads for connecting the resistive coil to the power connecting unit at both ends of the heater.
Preferably, a longitudinal section of the heater is substantially rectangular.
Preferably, each of the leads comprises: a metal terminal having one end connected to the resistive coil, and extending outward from the bottom of each end of the heater; and a first insulator covering the bottom of each end of the heater.
Preferably, each of the leads comprises: a molybdenum thin film having one end connected to the resistive coil; a metal terminal connected to the other end of the molybdenum thin film; a second insulator enclosing the molybdenum thin film and each end portion of the heater; and a first insulator located inside a second insulator and below the bottom of each end of the heater.
Alternatively, each of the leads may comprise: a molybdenum thin film having one end connected to the resistive coil; a molybdenum wire having one end connected to the other end of the molybdenum thin film; a metal terminal connected to the other end of the molybdenum wire; a second insulator enclosing the molybdenum thin film and each end of the heater; and a first insulator located inside a second insulator and below the bottom of each end of the heater.
Alternatively, each of the leads may comprise: a metal terminal having one end connected to the resistive coil; a metal pipe enclosing each end of the heater and a portion of the metal terminal, and welded to the metal layer; and an insulator located in a space between the metal pipe and the metal terminal.